Field of the Invention
The present invention relates generally to a method for controlling a cooling system in a vehicle and, more particularly, to a method for controlling a cooling system in a vehicle, which optimizes a coolant temperature according to whether to use EGR or NOx emissions to increase fuel efficiency and to reduce NOx emissions.
Description of Related Art
Developing a fuel-efficient and eco-friendly vehicle has become more important due to worldwide fuel efficiency regulations and regulations limiting CO2 emissions. Leading automakers have actively researched and developed techniques for reducing vehicle fuel consumption to achieve the above goal.
Under cold conditions immediately after starting a vehicle, fuel efficiency is low even though the engine is sufficiently warmed up. That is because a high viscosity of oil increases engine friction, heavy heat loss occurs due to a low temperature of a cylinder wall, and combustion stability is decreased.
Consequently, for an increase in fuel efficiency of a vehicle, improvement in engine durability and improvement in EM (Emissions), it is necessary to quickly raise the temperature of the engine to a normal temperature when starting a vehicle.
FIG. 1 is a simplified diagram of a cooling system according to a conventional art.
Referring to FIG. 1, for controlling coolant at an outlet, a water pump 102 is installed at an inlet of an engine 101. Some of the coolant that has come into the engine 101 through the water pump is moved to an oil cooler and goes through the engine block and head. Also, a coolant temperature sensor 103 for measuring a temperature of the coolant is arranged in front of a coolant flow control valve 104.
In the cooling system configured as described above, a method for quickly raising the temperature of the coolant immediately after starting a vehicle is suggested. The method controls an amount of flow or flow channels using the coolant flow control valve 104, or performs Zero flow control that stagnates the coolant inside the engine using a clutch water pump, etc. so as not to remove heat generated inside the engine and to store the heat in the engine so as to quickly raise the temperature of the coolant. Also, after warming up the coolant, the method maintains the temperature of the engine to be higher than the previous engine temperature by controlling the raising of the coolant temperature so as to reduce heat loss and friction for improvement in fuel efficiency.
However, the above method has a problem of increased NOx production. Accordingly, to achieve improvement of fuel efficiency through controlling the raising of the coolant temperature, a target temperature of the coolant should be controlled so that the improvement of the fuel efficiency exceeds the increase of NOx.
In this case, the target temperature for the coolant may be set based on a map according to an engine operating condition (rpm/a fuel use amount).
However, if the raising of the coolant temperature is controlled based on one map, it is difficult to reach the target EM level or target fuel efficiency due to variations in the surrounding environment or deterioration of the engine hardware.
For example, when an engine is operated in an EM region using EGR (Exhaust Gas Recirculation), which is an operation point of a mode used for measurement of exhaust gas, there is a limit to raising the engine temperature due to increased NOx levels, while in the high-speed, high-load non-EM region in which typically EGR is not used, it is possible to raise the temperature of the coolant within the endurance limit of the engine. Accordingly, if the raising of the coolant temperature is controlled based on one coolant temperature map without regard to whether to use EGR or NOx emissions, chances of improving the fuel efficiency may decrease.
The information disclosed in this Background of the Invention section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.